1. Field of the Invention
This invention relates to the repair of superalloy articles and, more particularly, to a method and alloy powder mixture for the repair of nickel-base and cobalt-base superalloy articles.
2. Description of the Prior Art
A variety of high temperature superalloys of the nickel-base or cobalt-base types are used in a variety of components in the high temperature operating section of gas turbine engines. As a result of the strenuous operating conditions, damage or deterioration in the form of cracks or other discontinuities, including other openings, can occur such as from thermal cycling or impact from airborne foreign objects or their combinations. In other instances, cracks in such high temperature superalloy components can occur during their manufacture. Because of the relatively high cost of such superalloy components, it is desirable to repair rather than to replace such articles.
One method for cleaning and repairing superalloy articles is described in U.S. Pat. No. 4,098,450-Keller et al issued July 4, 1978 and assigned to the assignee of the present invention. Described is a method using fluoride ions to contact oxide in a narrow crack or crevice to convert the oxide to gaseous fluoride. Subsequently, in one form of the invention, a repair alloy is applied to repair the crack or crevice.
In other repair methods which have been used for many years in the gas turbine engine art, oxides have been removed from parts to be repaired by mechanical means, or, predominantly in the case of cobalt-base alloys, through the use of hydrogen prior to application of a brazing alloy of the single alloy or wide-gap brazing mixture type. Such wide-gap brazing alloys have been described in the art, for example in U.S. Pat. No. 3,155,491-Hoppin et al issued Nov. 3, 1964.
Currently in use in gas turbine engines are cobalt-base alloy combustors one type of which is made from a cobalt-base alloy commercially available as HS188 alloy and consisting nominally, by weight, of 0.1% C, 22% Ni, 3.5% Fe, 22% Cr, 2% Mn, 0.4% Si, 15.5% W with the balance Co and incidental impurities. It has been observed that such a combustor can develop a number of small cracks while in or resulting from strenuous service. Currently, such cracks are repaired by welding. Sometimes repetitive repair welds are necessary in the same area because cracking also can occur during the repair operation. Heretofore, a powder alloy system capable of being used to repair such cracks by a method similar to vacuum brazing has not been reported.